In dialysis, and particularly in hemodialysis, the rate of ultrafiltration (water removed from the solution to be dialyzed) is a critical matter, and one which particularly must be carefully controlled during a blood dialysis procedure with a patient.
Currently, ultrafiltration can be calculated from the mean dialyzer pressure differential between the blood flow path and the dialysis solution flow path by taking the arithmetic mean of the overall dialyzer pressure. This however requires the measurement of pressure both at the dialysis solution inlet and the outlet, and additional equipment to accomplish it. Also, it is not necessarily an accurate way to measure ultrafiltration, particularly in the case where for any of various reasons the integrated sum total area of the dialyzer pressure differential is not equal to arithmetic mean pressure differential.
Another technique for measuring ultrafiltration is to seal off the dialyzer and to shut off the blood pump, to get an integrated pressure as a direct read-out of pressure in the bubble trap of conventional dialysis blood line systems. It is, however, most undesirable to stop the blood pump during dialysis procedures.
The technique for measuring ultrafiltration utilized in this invention is a direct measurement of ultrafiltration over a limited period of time, without stopping of the flow of blood or other liquid to be dialyzed. Accordingly, from this data the overall ultrafiltration over a larger period of time can be extrapolated, with the results being reconfirmed from time to time by repeated testing of the ultrafiltration rate over a short period of time. The method of this invention may therefore be accomplished without complete halting of the dialysis procedure, and, with the apparatus of this invention, the testing for direct measurement of ultrafiltration may be conveniently performed at any desired time or times during the dialysis procedure.